Dry spinning of polyethylene



Oct. 5, 1965 --w.H.-|-lo-w-A-RD DRY SPINNING OF POLYETHYLENE Filed Nov. 6, 1962 INVENTOR ifilliamlfillowwd A ORNEY a spinneret directly into a coagulating bath.

United States Patent 3,210,452 DRY SPINNING 0F POLYETHYLENE William H. Howard, Cary, N.C., assignor to Monsanto Company, a corporation of Delaware Filed Nov. 6, 1962, Ser. No. 237,432 Claims. (Cl. 264-203) This application is a continuation-in-part of my copending application, Serial No. 846,150, filed October 13, 1959, now abandoned, and titled Dry Spinning of Polyethylene.

In the past, three basic types of spinning processes have been known for the production of fibers and filaments from ethylene polymers. These spinning processes are generally known as (1) melt spinning, (2) dry spinning, and (3) wet spinning. Each of these processes has certain inherent advantages and disadvantages with regard to each other, but none has been completely satisfactory for the production of low denier filaments of high tenacity.

In melt spinning, the polymer in powder or pellet form is melted and extruded through a spinneret in the shape of filaments which harden and are set up by contact with the cooling air surrounding the freshly extruded filaments. This method allows fairly high spinning speed, but requires considerable extrusion pressure and high melt temperatures. In addition, it has been found very difficult to melt spin polymers of high molecular weight since even at very high temperatures, the viscosity of the melt cannot be reduced sufiiciently to prevent clogging of the spinneret holes.

The dry spinning technique involves the extrusion of a solvent solution of polymer through a spinneret into a stream of heated gas to rapidly evaporate the solvent from the polymer and thus form the polymer filaments. This method also employs considerably higher spinning speeds than does the wet spinning method and, moreover, solutions of greater concentration can be employed than are used in the wet spinning method. However, large amounts of heat must be applied to the freshly spun filaments to remove the solvent, and this entails not only considerable expense but the amount of heat required may adversely affect the characteristics of the fibers.

In wet spinning, a polymer solution is extruded through In this method, filaments of lower denier may generally be produced, but spinning speed is far slower than in the previous two methods. In addition the composition and temperature of the coagulating bath must be carefully regulated in order to set up the freshly spun filaments, and remove the proper amount of solvent from them.

Generally the present invention is directed to a process for spinning ethylene polymer wherein a solution of the polymer is extruded through a spinneret which is situated a short distance above a liquid precipitation or quench bath. Only a small quantity of the solvent contained in the polymer solution is evaporated while traversing the short distance between the spinneret and the quenching liquid, the remainder of the solvent being substantially completely removed by contact with the precipitation or quench bath. The substantially solvent free filaments are directed over first drawing means so as to impart tension to the filaments between the extrusion nozzle or jet and the drawing means. The drawn filaments are then passed through a second body of liquid and over a second set of drawing means in order to impart further tensioning and drawing of the filaments. The thus drawn and oriented filaments are then wound upon a bobbin or otherwise collected for further processing.

The process of this invention offers numerous advantages over the above discussed prior art methods. As compared to melt spinning, the instant process may be utilized to spin ethylene polymer of far greater molecular weight. In general, the ethylene polymers suitable for the spinning process of this invention have a melt index ranging from 0.4 to 20.0 and a molecular weight ranging from about 20,000 to 200,000. (Melt index is a standard measurement defined in ASTM part 6 (1955) pages 292 295, identification number D-l238-52-T.)

Unlike dry spinning, the present method does not require expensive equipment and large quantities of heat to evaporate solvent from the freshly spun filaments. In fact, spinning is usually conducted at room temperature.

In comparison to Wet spinning, the method of this invention offers higher spinning speeds, and avoids the necessity for critical control of the temperature and composition of a coagulating bath.

It is an object of this invention to provide a process for spinning ethylene polymers into filaments, fiber, rods and the like.

It is a further object of this invention to provide a process for spinning ethylene polymers into filaments of high tenacity and low denier.

It is further an object of this invention to provide a spinning process for the conversion of ethylene polymers to filaments, fiber and the like which is relatively inexpensive and simple.

It is a further object of this invention to provide a process which produces filaments with excellent textile characteristics at a high speed.

Other objects and advantages of the invention will become apparent to those skilled in the art from consideration of the following detailed description and accompanying sheet of drawing in which:

The single figure is a schematic elevational View show ing an arrangement of apparatus which may be suitably employed for carrying out the process of the present invention.

Referring now to the drawing, an organic solvent solution of ethylene polymer, referred to as dope, is passed under pressure from an inert gas, such as nitrogen, from a heated hold tank (not shown) where the polymer solution is received from a polymer dissolving means (also not shown) through conduit 2 and then through a filter 4 which removes undissolved particles and foreign materials from the solution. The dope passes through conduit 5 and then through the spinneret assembly or jet 6 and out of spinneret 8 which is shown mounted a short distance above a quench liquid 10 contained in quench bath 12. A heater 11 is employed to maintain the jet assembly at a temperature sufficient to prevent precipitation of the polymer from solution. The dope in passing through the one or more orifices inthe spinneret 8 forms a filament or bundle of filaments 9 which is passed around filament guide 14 located beneath the surface of the quench liquid and thence over second filament guide 20 to a pair of rollers 22 and 23 or other thread advancing means. The quench 12 is provided with inlet pipe 16 and overflow conduit 18 for the introduction and withdrawal of quench liquid.

Rollers 22 and 23 are positively driven and exert an attenuating force upon the filament or bundle of filaments. This first drawing of the filaments is termed a jet stretch. The magnitude of tension applied in a drawing operation of this type is generally expressed in terms of the jet stretch ratio, which is defined as the rate of filament take up divided by the extrusion rate. Thus, in the instant invention, the jet stretch ratio is determined by dividing the rate of take up of rollers 22 and 23 by the rate of extrusion from spinneret 8. This value can be greater than 1, less than 1, or 1.

After passing around rollers 22 and 23, the filament or bundle of filaments is then directed over filament guide 26 and filament guide 28 located in a stretch bath 24 containing an aqueous stretch liquid 30, from whence the filament line is passed around filament guides 32 and 34 over a second set of positively driven rollers 36 and 38 and finally to wind up roll 40. The rollers 36 and 38 are given a peripheral speed greater than that of the rollers 22 and 23 so as to draw or impart a stretch to the filament or filaments passing through the bath 24. Liquid is continuously introduced to the stretch bath through inlet pipe 42, and withdrawn through outlet pipe 44.

As described above in connection with the drawing, tension is imparted to the ethylene polymer filament or filaments at two stages in the instant process. It has been found that the tenacity of the fibers produced is directly related to the amount of tension applied and particularly to that imparted in the stretch bath or second stage. Higher tenacities are obtained by limiting the first or jet stretch to from about to about 50 percent of maximum, and preferably percent of maximum, While maintaining the second stretch at from about 50 to about 95 percent maximum with about 90 percent of maximum being preferred. The maximum stretch is, of course, that degree of stretch just short of the breaking point of the filament or filaments. It is not a fixed value but will vary with such factors as type of ethylene polymer, solvent used, bath temperatures, quenching medium and other Variables.

The stretching operation serves to reduce the diameter of the filament or filaments as well as to orient the molecules of the fiber to give increased tenacity.

By limiting the jet stretch to below about 50 percent and preferably at about 30 percent of maximum, greater stretching of the filaments in the stretch bath may be achieved with subsequent higher tenacities. When employing a jet stretch of 30 percent of maximum and a second stretch of 90 percent of maximum, polyethylene filaments with tenacities of 8 grams per denier have been spun.

In the specification and claims herein, the term ethylene polymers is intended to include not only polyethylene itself, but also copolymers and terpolymers of ethylene, and blends of polyethylene and copolymers of ethylene with other polymerizable mono-olefinic materials wherein the polyethylene is present in a predominant amount, as about 80 percent or more. Examples of suitable mono-olefinic materials which may form copolymers or terpolymers with ethylene are such mono-olefins as propylene and butylene, halogenated ethylene such as vinyl chloride, vinylidene chloride, tetrafluoroethylene and vinylidene fluoride, vinyl ethers, ketones and esters, such as methyl vinyl ether, methyl and ethyl vinyl ketones, vinyl chloroacetate, vinyl propionate, and vinyl acetate, styrene, N-vinylphthalimide, acrylic and methacrylic acids, their esters, nitriles, amides and imides, and other compounds containing the C=C groups such as esters of rnaleic and fumaric acids and esters of itaconic acids. It is to be understood, of course, that these polymers may be admixed with other additive ingredients such as pigments, plasticizers, fillers, antioxidants and the like.

In preparing the spinning solution or dope of the present invention, the ethylene polymer is preferably stirred into the heated solvent and mixed for about one hour or until the polymer goes into solution. The dope is then allowed to remain quiescent while maintained at a sulficiently elevated temperature to keep the polymer in solution for about an hour or more for deaeration.

The solvents employed in preparing the dope are critical, that is they must meet certain definite requirements to be operable in the practice of this invention. Among these requirements is that the solvent must be capable of remaining in the liquid state down to a temperature of 0 C. In addition the solvent must be incompatible with the ethylene polymer solute at temperatures in the range of from 0 C. to 50 C. That is, the solvent must separate from the ethylene polymer in this temperature range.

A further critical feature of the solvent is that it has a boiling point in the range of from 109 C. to C. Also the solvent at these temperatures should give a moderately viscous dope having a solid content above about 20 percent. The boiling point must be above about 109 C. because the spinning temperatures employed in the process are generally within this range; while solvents with boiling points above about 150 C. do not tend to separate from the polymer at the coagulation temperatures employed.

Solvents which eminently meet the foregoing critical requirements are the alkyl derivatives of benzene, more specifically, the methyl substituted benzenes. These include toluene and the three isomeric xylenes, i.e. ortho, meta and para-xylene. Any of these compounds are suitable either when employed alone or in admixture.

Another variable which is important with regard to the obtaining of fibers with good tenacity is the extent of elevation of the spinneret above the quench bath. In general, it has been found that best results are obtained when the elevation of the spinneret above the quench bath is maintained at from about Me of an inch to about 2 inches. These values may be varied somewhat depending upon the particular type of ethylene polymer being spun, the ambient temperature surrounding the freshly extruded filaments and the amount of jet stretch imparted to those filaments. The lower limit of A; inch is chosen primarily for practical reasons, in that if the spinneret is maintained too close to the surface of the quench liquid, then said liquid may creep onto the spinneret through capillary action and interfere with the extrusion of the dope.

With regard to the maximum height of elevation of the spinneret, it has been discovered that too great an elevation leads to the production of brittle filaments which are opaque and white in color. Though the reason for this whiteness and opaqueness is not completely understood, it appears to be related to a crystallization phenomenon. When the freshly extruded polymer passes through the ambient and unheated atmosphere over too great a distance, significant evaporation of the solvent occurs and the polymer starts to crystallize. Though this crystallization phenomenon also may be related to such factors as the ambient temperature and the amount of jet stretch, it is most easily avoided by lessening the elevation of the spinneret. Accordingly, the maximum elevation above the quench liquid is that distance at which the fibers; remain clear and easily stretchable, i.e., not brittle. Theoperator can easily lower the elevation when and if it should be noted that the filament is becoming opaque, white and brittle.

The quench liquids used in the present process are preferably of two types, namely (1) liquids which are miscible with the solvent in the ethylene polymer dope and (2) water. Among the liquids of the first type which may be used in the quench bath are benzene, isopropyl alcohol, chloroform and ether. In addition, the mate rials listed before as suitable solvents for the dope may also be employed as the quench liquid, i.e., xylene and toluene. Whether or not a liquid which is miscible with the dope solvent or water is used as the quench liquid will depend not only on the type of ethylene polymer being spun but on the filament properties desired. Generally speaking, water has been found to be the preferred quench liquid for several reasons. In the first place, it is, of course, the most economical quench liquid which can be used. Moreover, it has been found that the preferred dope solvents are effectively removed from the spun fibers and collected upon the surface of the water for simple collection as by decantation. In the illustrative apparatus of the drawing, the dope solvent which is collected on the surface of the water is continually removed by overflow through conduit 18. Finally, it has been found that the use of a water quench bath allows greater attenuation in the subsequent stretch bath than is the case with other liquids.

The temperature of the quench bath may vary from 0 C. to 40 C. Though the exact explanation as to what happens to the freshly extruded fibers as they pass into the quench bath is not entirely clear, it is known that the primary phenomenon is one of squeezing out of the dope solvent, i.e., the solvent is separated from the fiber at this point. This is caused primarily by the reduced solubility of the polymer at the temperatures of the quench bath which are considerably lower than the spinning temperatures. It is believed that the short path of travel through the air prior to entrance into the quench bath minimizes evaporation of solvent in air and reduces the tendency of the polymer to crystallize, thereby permitting subsequent stretching and orientation of the molecules within the filament. When the quench bath is omitted and air is used as the quenching medium, it has been found that the filament or filaments can be given a stretch of only about one-half as much, and the tenacities obtained are less than 40% of the tenacities produced with a water quench bath.

The stretch bath used in the instant process is preferably water heated to from about 60 to 100 C. with a range of 80 to 100 C. being preferred. In addition to providing the proper medium for stretching, the hot water stretch bath also serves to remove essentially all the remaining solvent from the fibers, that is about 3% which may remain after the passage through the quench bath.

The spinneret used in accordance with the instant invention may be of the type ordinarily used in dry or melt spinning operations. spinning process is the orifice diameter of the spinneret. For practical reasons, it is always desirable to employ the largest diameter orifices consistent with good spinning. By increasing the orifice size, the filtration of the spinning solution becomes less important as the number of spinneret changes due to clogging of the holes thereof is reduced. In the present invention, one may employ orifices having relatively large diameters. This in practical terms means a reduction in operating costs. Among other benefits derived by employing large orifice openings are the higher spinning speeds possible, and the increased orientation of the fiber molecules due to the greater attenuation of the filaments that can be effected. In general, spinnerets with orifice opening of 2 to 20 mils in diameter have been successfully used. The spacing between the holes in the spinneret may be varied considerably without afiecting the spinning operation. Too close a spacing will, of course, lead to a running together of the filaments at the jet base. Generally speaking hole spacing of a minimum of about 0.020 inch has been found satisfactory.

In order to describe further the present invention, the following specific examples are given, it being understood that the same are intended in an illustrative sense, and the invention should not be limited thereby. In the ex- A significant variable in any 6 amples, all parts and percentages are by weight unless otherwise indicated.

Example I Adope solution was prepared by heating a solution of Marlex 50 polyethylene (0.9 melt index) in xylene (25% solids content) at 120 C. with stirring for one hour. The solution was allowed to remain at 140 C. over night to allow complete deaeration. The dope was transferred to a hold tank maintained at 140 C. and forced under nitrogen pressure through a spinneret containing ten holes of 0.005 inch diameter. The spinneret was maintained at 110 C. during spinning.

The extruded filaments passed from the spinneret at 7 feet per minute and traveled through the 25 C. atmosphere of the room for one quarter inch before en tering a water quench bath maintained at 25 C. The filaments passed through the quench bath for about twelve inches before passing over the first set of drawing rollers and were then passed through a hot water stretch bath maintained at 100 C. for a distance of 24 inches before being taken up by the second set of draw rollers. Following the stretching operation the filaments were collected on a cone winder and tested for physical properties.

The operating conditions were as follows:

First roller, f.p.m. 28.0 Final roller, f.p.m. 207 Jet stretch ratio 4 Second stretch ratio 7.4 Percent of maximum jet stretch 30 Percent of maximum second stretch Tenacity (gm./ den.) 8.0 Elongation, percent 14 Denier per filament 1.04

In the above example, as in the examples which follow, the maximum jet stretch was determined by increasing the polymer take up rate in relation to the extrusion rate until filament rupture was observed. Thus, referring to the drawing, the rotation rate of rollers 22 and 23 were increased in relation to the extrusion rate at spinneret 3 until filament breakage occurred. In the above example, the jet stretch ratio was 13 at this point.

The maximum stretch in the stretch bath was determined in substantially the same manner as that of the maximum jet stretch. Thus, again referring to the drawing for illustration, the rotation rate of take up rollers 33 and 36 for stretch bath 24 was increased relative to stretch bath feed rollers 22 and 23 until filament breakage occurred. The stretch ratio at this point, in the instance of the above example, was 8.2.

Example 11 A dope was prepared in identically the same manner as described in Example I. Instead of using a water quench bath, the filaments were passed through the air at room temperature (25 C.) for 12 inches before being advanced over draw rollers for the first stretch. The same water stretch bath at C. was employed. The process was carried out under the following spinning conditions:

Extrusion speed, f.p.m. 7 First roller, f.p.m. 36 Final roller, f.p.m. 203 Jet stretch ratio 5.1 Second stretch ratio 5.6 Percent maximum jet stretch 30 Percent maximum second stretch 90 Tenacity (gm/den.) 4.1 Elongation, percent 75 Denier per filament 1.43

It is seen by comparing Example I to Example 11, that the fiber tenacity is almost double when. using a water quench bath as opposed to using air as the quenching medium.

Examples IIIVI Employing the same materials and techniques in the preparation of the dope, the following examples were carried out under the listed conditions. In all cases the quench bath was maintained at room temperature (25 C.), and a water stretch bath at 100 C. was used.

III IV V VI Quench bath Water Water Acetone Xylene Jet type (No. holes) (hole size) l/.0025 10/.0025" 10/.0050" 10/.0050" Jet elevation". V Extrusion speed, l.p.m 19 19 34 34 Jet stretch ratio 0. 35 0. 35 1.3 1. 3 Second stretch ratio 5. 8 10. 2 5. 7 5. 7 First roller speed, f.p.m 7. 7 7. 7 42. 8 42. 3 Final roller speed, f.p.m 44. 7 79. 0 245 245 Percent max. jet stretch 30 30 10. 5 10. 5 Percent max. second stretch 50 90 71 65 Tenacity (gm/den.) 3. 6 6. 6 2. 8 3. 5 Elongation (percent) 66 14 67 23 Denier per filament 4. O1 3. 03 2. 43 2. 93

Examples VII-VIII Jet temperature C.) 125 125 Jet type (No. holes) (hole size) 30/.0030" 30/.0030 Quench bath Water Water Jet elevation (in.) 1 1 Extrusion speed, f.p.m 17 53 Jet stretch ratio 1. 4 0. 47 Second stretch ratio. 8. 0 8. 0 First roller speed, f.p 25. 0 25. 0 Final roller speed, f.p.1n 200 200 Tenacity (gar/den.) 6. 7 3. 8 Elongation (percent) 20 50 Denier per filament 1. 1 4. 8

From the foregoing general discussion and detailed description it will be evident that this invention provides a process for the spinning of ethylene polymer which is rapid, requires minimum critical controls and produces filaments, rod and the like of excellent tenacity. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A process for fabricating ethylene polymer filaments comprising the following steps: intermixing an ethylene polymer with a solvent consisting of a methyl substituted benzene compound having a boiling point in the range of from 109 C. to 150 C. and which is incompatible with the ethylene polymer at temperatures in the range of from 0 C. to 50 C., to obtain a solution containing at least 20 percent by weight of said polymer, extruding said solution at elevated temperatures through shaped orifices and thence into the atmosphere, passing the extruded polymer solution through the atmosphere a distance of from about inch to about 2 inches, and then introducing the extruded polymer solution into a quench bath maintained at a temperature of from 0 C. to 40 C. to form the polymer filaments, drawing the filaments as they are formed in the quench bath, and thereafter 8 passing the filaments from said quench bath to a heated aqueous bath and drawing said filaments in the heated aqueous bath to a greater extent than previously.

2. A process for fabricating ethylene polymer filaments comprising the following steps: intcrmixing an ethylene polymer with a solvent consisting of xylene to obtain a solution containing at least 20 percent by weight of said polymer, extruding said solution at elevated temperatures through shaped orifices and thence into the atmosphere, passing the extruded polymer solution through the atmosphere a distance of from about /8 inch to about 2 inches, and then introducing the extruded polymer solution into a quench bath maintained at a temperature of from 0 C. to 40 C. to form the polymer filaments, drawing the filaments as they are formed in the quench bath from about 10 percent to 50 percent of maximum, and thereafter passing the filaments from said quench bath to a heated aqueous bath and drawing said filaments in the heated aqueous bath to from about 50 percent to 90 percent of maximum.

3. The process of claim 2 wherein the quench bath contains water.

4. The process of claim 2 wherein the quench bath consists of a solvent miscible with the solvent contained in the polymer solution.

5. The process of claim 2 wherein the ethylene polymer has a melt index ranging from about 0.4 to 20.0 and a molecular weight ranging from about 20,000 to 200,000.

6. A process for fabricating ethylene polymer filaments comprising the following steps: intermixing an ethylene polymer with a solvent consisting of a methyl substituted benzene compound having a boiling point in the range offrom 109 C. to 150 C. and which is incompatible with the ethylene polymer at temperatures in the range of from 0 C. to 50 C., to obtain a solution containing at least 20 percent by Weight of said polymer, extruding said solution at elevated temperatures through shaped orifices and into the atmosphere, passing the extruded polymer solution through the atmosphere a dis tance of from about Ms inch to about 2 inches, and then introducing the extruded polymer solution into a quench bath maintained at about 0 to 40 C. to form the polymer filaments, drawing the filaments as they are formed in the quench bath to from about 10 percent to 50 percent of maximum, and thereafter passing the filaments from said quench bath to an aqueous bath maintained at about to 100 C. and drawing said filaments in the heated aqueous bath to from about 50 percent to percent of maximum.

7. A process for fabricating ethylene polymer filaments comprising the following steps: intermixing an ethylene polymer with a solvent consisting of xylene to obtain a solution containing at least 20 percent by weight of said polymer, extruding said solution at elevated temperatures through shaped orifices and into the atmosphere, passing the extruded polymer solution through the atmosphere a distance of from about inch to about 2 inches, and then introducing the extruded polymer solution into a quench bath maintained at about 0 to 40 C. to form the polymer filaments, drawing the filaments as they are formed in the quench bath to from about 10 percent to 50 percent of maximum, and thereafter passing the filaments from said quench bath to an aqueous bath maintained at about 80 to C. and drawing said filaments in the heated aqueous bath to from about 50 percent to 90 percent of maximum.

8. The process of claim 6 wherein the quench bath contains water.

9. The process of claim 6 wherein the quench bath consists of a solvent miscible with the solvent contained in the polymer solution.

10. The process of claim 6 wherein the ethylene polymer has a melt index ranging from about 0.4 to 20.0

9 and a molecular Weight ranging from about 20,000 to 200,000.

References Cited by the Examiner UNITED STATES PATENTS 2,210,771 8/40 Myles 1854 2,367,493 1/45 Fordyce et a1. 18-54 2,953,818 9/60 Bartron 18-57 1 0 FOREIGN PATENTS 1,024,201 2/5 8 Germany. 1,040,179 10/58 Germany.

845,374 8/60 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

MORRIS LIEBMAN, ROBERT F. WHITE, Examiners. 

1. A PROCESS FOR FABRICATING ETHYLENEN POLYMER FILAMENTS COMPRISING THE FOLLOWING STEPS: INTERMIXING AN ETHYLENE POLYMER WITH A SOLVENT CONSISTING OF A METHYL SUBSTITUTED BENZENE COMPOUND HAVING A BOILING POINT IN THE RANGE OF FROM 109*C. TO 150*C. AND WHICH IS INCOMPATIBLE WITH THE ETHYLENE POLYMER AT TEMPERATURES IN THE RANGE OF FROM 0*C. TO 50*C., TO OBTAIN A SOLUTION CONTAINING AT LEAST 20 PERCENT BY WEIGHT OF SAID POLYMER, EXTRUDING SAID SOLUTION AT ELEVATED TEMPERATURES THROUGH SHAPED ORIFICES AND THENCE INTO THE ATMOSPHERE, PASSING THE EXTRUDED POLYMER SOLUTION THROUGHT THE ATMOSPHER A DISTANCE OF FROM ABOUT 1/8 INCH TO ABOUT 2 INCHES, AND THEN INTRODUCING THE EXRUDED POLYMER SOLUTIN INTO A QUENCH 